Modern concepts of membrane structure envisage a lipid bilayer "sea" in which float "icebergs" of glycoprotein and glycolipid. In the plasma membrane, carbohydrate has a polar distribution towards the external environment. A popular theory suggests that the structurally diverse oligosaccharides on the external surfaces of cells are involved in membrane-mediated information transfer, i.e, they function as identity signals in cell-cell interactions. The process which converts an undifferentiated stem cell into a highly differentiated mature sperm is called spermatogenesis and requires interactions between individual germ cells, between germ cells and Sertoli cells, and between germ cells and the surrounding liquid environment. Surface sugars almost certainly play important roles in this differentiation process. This laboratory has for the past 11 years specialized in complex carbohydrate assembly by mammalian liver. In search of a role for surface sugars in differentiation, we began 3 years ago analogous studies on mammalian testis. Support for this work came from NIH; renewal of this grant for a further 3 years is the purpose of the present application. (1) Glycoprotein metabolism: Our previous studies on glycoprotein glycosyltransferases in whole testis will be extended to isolated germinal and Sertoli cell preparations. We will seek qualitative and quantitative differences in the transferases of different cell types. We also hope to study the transferase distribution and glycoprotein composition of subcellular fractions from these isolated cells. The biogenesis of membrane glycoproteins will be studied by using radioactive precursors such as fucose. (2) Glycolipid metabolism: We have published several studies on the testis-specific glycolipid, 1-O-palmityl-2-O-palmitoyl-glyceryl-3-beta-D-galactopyranoside sulfate (sulfogalactoglycerolipid, SGG). We have good evidence that its major and possibly sole site of synthesis is the Golgi apparatus of spermatocytes. We plan further studies to establish its cellular and subcellular sites of synthesis, its fate during spermatogenesis and its role, if any, in spermatogenesis and fertilization.